Improved screw-tap



Cd'thttetl 5mm @met @time Letters Patent No. 98,943, (lated January 18,1870.

IMPROVED SCREW-TAP.

The Schedule referred to in these Lettere Patent and making part of thename.

To all whom it may concern;v4

Be it known that I, CHRISTIAN L. FEHRENSEN, of the city, county, andState of New York, have invented a new and improved Screw-Tap; and I dohereby declarethe following to be a full, clear, and exact descriptionthereof, which will enable those skilled iri the art to make, and usethe same, reference being had to the accompanying drawing, formingpartof this specilioation, iu which drawing- Figure 1 represents a frontview of this invention.

Figure 2 is a longitudinal section thereof'.

`Similar letters indicate corresponding parts.

This invent-ion relates to a screw-tap, provided with a single dat face,cut down` at its deepest place to the centre (or nearly so) of the tap,and .ruiming up in a gradual curve to the circumference of said tap, incombinat-ion with a round guiding-nipple, formed bythe body of the tap,between its tapering end and the flat face, in such a manner, that bysaid fiat face two sharp cutting-edges are' produced, and that a singletap is suilcient to'cut a-deep and perfect thread, said tap being heldin lthe proper position, at the commencement of the operation, by theguiding-nipples.

The letter A designates a screw-tap, vwhich is made tapering toward. itsend a, so that` on said end the screw-threadis eutirelycut away, whileon the upper part of said tap the thread is left intact, as shown.

Said tap is provided with a single at face, @which is cut down to thecentre of the tap, or nearly so, and

runs up in a gradual curve to the circumference thereof, as seen in thedrawing, so that two sharp cutting-V edges, c, are produced,`whichmaterially assist in forming the thread in the nut to be tapped.

That portion of the tap below the at face is left round, `so as to forma guiding-nipple, d, which serves to keep the tap in the proper positionat the commencement of the operation.

l By these means a screw-tap is obtained, which allows of cutting aperfect thread by a single operation, while with taps of the usualconstruction two or three different taps are required to obtain thedesired result. It is obvious that my improvement is applicable to tapswith at threads, as well as to such with V- shaped threads.

What 1 claim as new, and desire to `secure by Let-y

